Saponin is an amorphous glycoside which is abundantly present in soybeans, azuki beans, olive, and the like. Saponin is named since it has a hydrophobic portion and a hydrophilic portion and forms persistent bubbles when mixed with water and shaken.
Saponin is broadly classified into steroid saponin and triterpenoid saponin according to the type of aglycone. The soyasaponin is contained abundantly in soybeans (glycine max), particularly in a soybean hypocotyl, and is a kind of the triterpenoid saponin Soyasaponins are mainly composed of soyasaponin Aa, Ab, Ac, Ad, Ae, Af, Ag, and Ah each having soyasapogenol A as the aglycone (hereinafter referred to as “soyasaponin group A glycoside”) and soyasaponin I, II, III, IV, and V each having soyasapogenol B as the aglycone (hereinafter referred to as soyasaponin group B glycoside) (Non-Patent Literature 1).
As the efficacies of soyasaponins, anti-obesity, blood neutral lipid reduction, cholesterol lowering effect, hepatoprotective action, antiviral activity, and the like have been known.
Soyasaponins having a high group B content are more effective for suppressing an increase in blood neutral lipid as compared to soyasaponins having a high group A content. The effect of suppressing blood glucose level increase is not observed with soyasaponin group A but is observed with soyasaponin B group. It is considered that the reason for the high activity of the soyasaponin group B resides in the absorption of the group B which is higher than that of the group A.
Soyasaponin aglycone obtained by removing sugar chain residues from soyasaponins is known to have a hyaluronic acid production promotion effect and a melanin production suppression effect of skin cells as well as a collagen production promotion effect. Also, 3-O-D-glucuronopyranosyl soyasapogenol B in which glucuronic acid is attached to the aglycone is known to have an anti-oxidant ability.
A further improvement in bioactivity can be expected from a further improvement in absorption of the soyasaponin group B. In order to improve the absorption of soyasaponin B group, it is contemplated to change the glycoside of the soyasaponin group B to the aglycone, i.e. to soyasapogenol B. As methods for producing the soyasapogenol B, a method using high pressure hot water, a method utilizing enzymatic decomposition, a chemical synthesis method, and the like are known.
However, in comparison of absorption between glycoside and aglycone of soybean isoflavone, it has been reported that aglycone has better absorption, and, on the other hand, it has been reported that there is no difference in absorbance. Whether there is the difference in absorption between glycoside and aglycone of soyasaponin or not has not been investigated yet.